I just received an email from Zillow that says my house is worth $811,000. How does Zillow know that and is it accurate? Nobody from Zillow has been to my house. - Tim B.
According to Zillow's website, Zillow uses a proprietary formula to estimate market value. Their site clearly states that it is not an appraisal and merely a starting point for determining the value of their home. If you want a better idea of what your home is worth, you can ask a real estate agent for a comparative market analysis (CMA) or hire an appraiser to perform an appraisal on your house, much like a bank would during a purchase or refinance.